As a method for manufacturing a silicon single crystal, the Czochralski method is known. According to this method, a raw material lump is contained in a quartz crucible installed in a chamber and heated by a heater, and the raw material in the crucible is turned to a melt. Further, a seed crystal is contacted with a raw material melt surface and pulled while being rotated, and a silicon single crystal having a desired diameter and quality is grown.
In a process of manufacturing a silicon single crystal, in order to eliminate a dislocation contained in the seed crystal or a dislocation generated by heat shock at the time of liquid contacting or the like, the diameter is once narrowed to approximately 3 to 4 mm in a Dash-necking process to form a neck portion.
Then, a straight body portion which turns to a product is formed through a corn process of gradually increasing the diameter to a desired diameter. At last, in order to reduce an influence of a dislocation due to the heat shock caused at the time of separating from the silicon melt, a tail portion having a reduced diameter is formed and separated from the silicon melt.
However, in the process of manufacturing a silicon single crystal, a dislocation is generated in the corn process or the straight body process due to various disturbances in some situations. In this case, since single-crystallization of a crystal formed in a subsequent process is impaired, a value as a product is lost. Thus, if a dislocation is generated in an early stage in the silicon single crystal manufacturing process, a single crystal manufactured thus far is again molten (which will be referred to as remelting hereinafter), and then manufacture of the single crystal is again performed.
In a process of remelting, a temperature of the melt is increased to a temperature at which the crystal is molten. Then, the crystal is immersed in the melt and molten. At this time, since attention must be given such that the crystal does not come into contact with a crucible bottom portion, it is preferable to immerse the crystal in the range of approximately 20 to 50 mm. After confirming that the immersed crystal is molten, an operation of likewise immersing the crystal in the melt is repeated, and all manufactured crystals are molten.
In a method for manufacturing a silicon single crystal disclosed in Patent Document 1, as means for efficiently remelting a crystal in which a dislocation has occurred, a method for immersing the crystal at a fixed average velocity while applying vibration of vertical movement thereto is described.